The principal goal of this unit continues to be the biochemical characterization of eukaryotic and animal viral genes. Attention has been focussed on the segments of papovavirus and murine leukemia virus genomes responsible for the establishment and maintenance of the transformed state. In this regard, the portions of polyoma virus DNA mediating tumorigenesis has been delineated and the structure and intracellular location of the protein kinase activity of viral middle T antigen has been investigated. A subgenomic segment of AKR ecotropic murine leukemia provirus, that specifically reacts with the envelope region of endogenous ecotropic retroviruses, has been cloned in E. coli and used as a probe to identify such sequences in normal mammalian DNAs. SV40 DNA recombinants containing mouse and human globin genes and the human growth hormone gene have been constructed and the gene products produced in monkey kidney cells evaluated. Risk assessment experiments involving EK1 derivatives of E. coli K12 containing oligomers of polyoma DNA, Harvey sarcoma virus and dilysogens of polyoma DNA were initiated.